Smart antenna for interference rejection with enhanced tracking

ABSTRACT

A smart antenna system is provided for communicating wireless signals between a mobile device and a plurality of different fixed base stations using one or more channels and one or more beams. The smart antenna system includes a control subsystem, a radio transceiver and an antenna subsystem coupled to each other and adapted to perform scanning of one or more combinations of base stations, channels and beams using one or more test links established with one or more of the fixed base stations where the test links use at least some of the channels and the beams. A first combination of base station, channel and beam is selected based on the scanning; and a first operating link is established for transmitting a wireless signal to the selected base station using the selected channel and beam.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of and claims priority toU.S. application Ser. No. 13/644,852, filed Oct. 4, 2012, which ishereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

This invention is directed towards antenna systems for mobile devices.

BACKGROUND OF THE INVENTION

Wireless communication is extensively used in mobile or nomadicapplications.

In a typical mobile/nomadic application, a mobile or nomadic wirelessdevice or mobile station will try to establish a link with a fixed basestation, so as to transmit information to the base station. To achievecoverage of the desired area, multiple base-stations must be used. FIG.1 shows an example of a system used to support a mobile application.Mobile station 111 will try to establish a link with one of basestations 121 and 122, as it travels along path 131.

Typical solutions for mobile or nomadic wireless devices useomnidirectional antennas that are isotropic or have similar properties,for example gain, in all directions of interest.

While mobile/nomadic devices use omnidirectional antennas, strictseparation between base-stations covering adjacent areas is required toavoid harmful self-interference. Separation can be achieved through:

Time, that is, the base stations do not transmit and receive at the sametime,

Frequency, that is, the base stations transmit and receive on differentfrequencies, or

Code, that is, the base stations transmit and receive using differentcodes.

All these methods reduce the total system capacity.

FIG. 2 shows an example of the coverage 403 for base-station 401 and thecoverage 404 for the base-station 402 when both base-stations use thesame frequency channel, and the three mobile/nomadic devices 406, 407and 408 use omnidirectional antennas. This assumes there are no othertime or code methods used to reduce interference between the twobase-stations 401 and 402. As can be seen, much of the area of interest405 is not adequately covered. Mobile device 406 receives coverage, thatis, it can establish an operating link with better than threshold signalquality from base station 401 in area 403. Similarly mobile device 407receives coverage from base station 402 in area 404. However, mobiledevice 408 cannot receive coverage from either base station 401 or 402because the signal quality is not good enough. This is because theomnidirectional antenna captures signals from the two base-stations 401and 402 and needs to be very close to one of them and very far from theother to obtain the needed signal quality.

In order to solve the problem shown in FIG. 2, there is a need for asystem that has omnidirectional coverage, but is able to focus on onesector so as to optimize signal quality to enable communications withthe highest reliability. Until now, systems have focused on optimizingsignal strength, which may not result in enabling communications withthe highest reliability.

SUMMARY OF THE INVENTION

In accordance with one embodiment, a smart antenna system forcommunicating wireless signals between a mobile device and a pluralityof fixed base stations using one or more channels and one or more beams,said smart antenna system comprising a control subsystem, a radiotransceiver and an antenna subsystem coupled to each other and adaptedto perform scanning of one or more combinations of base stations,channels and beams using one or more test links established with one ormore of the fixed base stations and the test links use at least some ofthe channels and the beams. A first combination of base station, channeland beam is selected based on data obtained during scanning, and a firstoperating link is established for transmitting a wireless signal to thecurrently selected base station using the currently selected channel andbeam. After establishment of the first operating link, scanning iscontinued using one or more test links established with the currentlyselected base station, using one or more beams different from thecurrently selected beam and the currently selected channel, or with oneor more combinations of base stations, channels and beams. The continuedscanning is performed either periodically or aperiodically.

In one implementation, before the continued scanning is performed, saidcontrol subsystem inserts a downtime and the continued scanning isperformed during the downtime.

In one implementation, the control subsystem calculates the duration ofthe downtime before inserting the downtime.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may best be understood by reference to the followingdescription taken in conjunction with the accompanying drawings.

FIG. 1 shows an example of a system used to support a mobileapplication.

FIG. 2 shows example coverage of a given area for a mobile/nomadicdevice or station with an omnidirectional antenna.

FIG. 3 shows a smart antenna system.

FIG. 4 shows a radiation pattern for beam 200.

FIG. 5 shows an example radiation pattern for arrangement 300.

FIG. 6 shows a flowchart of the process when the smart antenna system100 becomes active.

FIG. 6A shows one embodiment for determining the operating channel andthe best-performing beam from a candidate set of channels and beams.

FIG. 6B is the flowchart of the process for another embodiment when thesmart antenna system 100 becomes active.

FIG. 6C shows a sequence of steps for the tracking process.

FIG. 6D shows a situation where mobile device 904 uses beam 906 toconnect to base station 901 to maximize signal to interference and noiseratio (SINR)

FIG. 6E shows a situation where after travelling in direction 907,mobile device 904 changes to beam 905 to connect to base station 901 tomaximize signal to interference and noise ratio (SINR)

FIG. 6F shows a situation where after further travel in direction 907,mobile device 904 changes to beam 906 to maximize signal to interferenceand noise ratio (SINR)

FIG. 6G shows beams 915A-915E produced by mobile device 904

FIG. 6H shows a sequence where tracking downtimes are inserted betweendata transmissions to allow switching between beam-channel combinationsto occur.

FIG. 7 shows an illustrative example of the advantage of makingselections of base station, operating channel and beam based on signalquality over signal strength.

FIG. 8 shows example coverage of a given area for a mobile/nomadicdevice or station with a smart antenna with the same base stations andthe same area of interest as in FIG. 2.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

Although the invention will be described in connection with certainpreferred embodiments, it will be understood that the invention is notlimited to those particular embodiments. On the contrary, the inventionis intended to cover all alternatives, modifications, and equivalentarrangements as may be included within the spirit and scope of theinvention as defined by the appended claims.

Turning now to the drawings and referring first to FIG. 3, FIG. 3 showsa smart antenna system 100 consisting of radio transceiver 101 totransmit over a wireless link; an antenna subsystem 102; and a controlsubsystem 103. Information can be passed between the radio transceiver101, antenna subsystem 102 and control subsystem 103. For example, thecontrol subsystem 103 can receive information, including, but notlimited to wireless link quality information; and other information suchas base station operating capacity and base station load/utilization;from either or both of the radio transceiver 101 and the antennasubsystem 102. The control subsystem 103 can process this informationand command either or both of the radio transceiver 101 and antennasubsystem 102 accordingly. The smart antenna system 100 is designed tobe installed in, for example, a mobile/nomadic device or station whichestablishes a wireless link to a base station.

The radio transceiver 101 performs several different functions,including but not limited to, for example, transmitting and receivinginformation on the available operating channels; obtaining data tocompute signal quality measures such as signal to noise ratio (SNR),signal to interference and noise ratio (SINR) and bit error rate (BER);and computing these measures either by itself or together with thecontrol subsystem 103. In one embodiment, the operating channel to beused for transmitting and receiving is set by the control subsystem 103.The radio transceiver can transmit on more than one channel. This allowsthe smart antenna system to have “background” operation. For example,while transmitting and receiving on a channel used in a currentoperating link in the foreground, the control subsystem 103 can directthe radio transceiver 101 to transmit and receive on other channels usedin, for example, test links which have been set up in the background.

In another embodiment, in addition to the signal quality measuresdescribed above, link quality measurements can also be computed. Theseinclude, for example, packet error rate (PER), packet jitter andthroughput.

The antenna subsystem 102 provides multiple beams that can be selectedby the control subsystem 103. The multiple beams can be produced byindependent antennas, by beam-steering or by beam-forming. Thesetechniques are well known to one having skill in the art.

Each beam provides nulls (directions in which signal is stronglyattenuated) that can be used to eliminate interference. FIG. 4 shows anexample radiation pattern of such a beam 200, where the main lobe 201 ofthe beam covers the 90° sector between lines 201-A and 201-B, while thelateral lobes 202 and 203 provide some attenuation and the back-lobe 204provides very strong attenuation.

The sum of the coverage of all beams provides omnidirectional coverage.FIG. 5 shows an example radiation pattern for such an arrangement 300,where the beam 200 of FIG. 4, with only main lobe 201 shown forsimplicity, is repeated 8 times as beams 301-308 at 45° intervals for360° coverage. Beams 301-308 are overlapping to ensure low ripple inomnidirectional coverage. The ripple 310 is the difference betweenmaximum gain and the minimum gain obtainable using all available beams.

The ability of the antenna subsystem 102 to provide multiple beamsallows for “background” operation on other beams. This, together withthe ability of the radio transceiver 101, to transmit and receive onother channels, means that the control subsystem 103 can establish testlinks in the background on different channels and beams, to the channeland beam used by the current operating link running in the foreground.

The control subsystem 103 is the controller of the smart antenna system100. The control subsystem 103 commands, controls, co-ordinates andmanages the operation of the antenna subsystem 102 and radio transceiver101. As explained previously, the control subsystem 103 can receiveinformation, such as wireless link status from either or both of theradio transceiver 101 and the antenna subsystem 102. When link status isactive, the control subsystem 103 can collect information related to,for example, signal quality; and other information such as base stationoperating capacity and base station load/utilization; from the radiotransceiver 101, or both the radio transceiver 101 and antenna subsystem102.

The control subsystem 103 can process this collected information andsend commands and control instructions to either or both of the radiotransceiver 101 and antenna subsystem 102 accordingly.

As previously explained, the control subsystem 103 collects informationrelated to signal quality. Various measures of signal quality can thenbe calculated. These measures include signal to noise ratio (SNR),signal to interference and noise ratio (SINR) and bit error rate (BER).As explained previously, in one embodiment the control subsystem 103collects this information, and then together with the radio transceiver101 calculates measures such as SNR, SINR and BER. In anotherembodiment, the radio transceiver 101 calculates these measures on itsown. In a further embodiment, the control subsystem 103 together withthe radio transceiver calculates a signal quality score for each basestation based on a function which takes in one or more of signal qualitymeasures such as SNR, SINR and BER as inputs, and produces the score asthe output. For example, in one embodiment the control subsystem 103calculates a weighted average based on SNR and SINR. In anotherembodiment, a weighted average is first calculated, then comparedagainst a threshold, and used to calculate a performance score. Thecontrol subsystem 103 can store also store historical signal qualityinformation, and other information for future use.

In another embodiment, in addition to the signal quality measuresdescribed above, as previously explained, link quality measurements canalso be calculated. These measures include, for example, packet errorrate (PER), packet jitter and throughput. Similar to signal quality, inone embodiment the control subsystem 103 collects this information, andthen together with the radio transceiver 101 calculates measures such asPER, jitter and throughput. In another embodiment, the radio transceiver101 calculates these measures on its own. In a further embodiment, thecontrol subsystem 103 together with the radio transceiver calculates alink quality score for each base station based on a function which takesin one or more of link quality measures such as PER, jitter andthroughput as inputs, and produces the score as the output. For example,in one embodiment the control subsystem 103 calculates a weightedaverage based on PER and jitter. In another embodiment, a weightedaverage is first calculated, then compared against a threshold, and usedto calculate a performance score. The control subsystem 103 can storealso store historical link quality information, and other informationfor future use.

In one embodiment, the control subsystem 103 is an independent module.In another embodiment, the control subsystem 103 is integrated with theother radio transceiver 101 control functions. The control subsystem 103can be implemented in hardware, software, or some combination ofhardware and software. In another embodiment, the control subsystem 103is installed as software on, for example, the radio transceiver 101.

When the smart antenna system becomes active, for example, when it is:

powered up;

returned from sleep; or

turned active by the user;

the control subsystem 103 then performs scanning of combinations of basestations, channels and beams, that is, it establishes test links to basestations with different channels and beams using the radio transceiver101 and the antenna subsystem 102, and performs analysis of resultsobtained from these test links to select the best combination of basestation, channel and beam.

FIG. 6 shows a flowchart of the process when the smart antenna system100 becomes active. In optional step 601, the control subsystem 103selects a subset of the available beams and channels before thecommencement of the scanning process, and then performs scanning usingthe selected subset. In one embodiment, control subsystem 103 selectsthe subset based on historical signal quality. As previously explained,signal quality can be measured by, for example, one of SNR, SINR andBER. As explained previously, in one embodiment the control subsystem103 together with the radio transceiver 101 calculates measures such asSNR and SINR. In another embodiment, the radio transceiver 101calculates these measures on its own. In a further embodiment, thecontrol subsystem 103 together with the radio transceiver 101 calculatesa signal quality score for each base station based on a function whichtakes in one or more of signal quality measures such as SNR and SINR asinputs, and produces the score as the output. For example, in oneembodiment the control subsystem 103 calculates a weighted average basedon SNR and SINR. In another embodiment, a weighted average is firstcalculated, then compared against a threshold, and used to calculate aperformance score.

In another embodiment, in addition to the signal quality measuresdescribed above, as previously explained, link quality measurements canalso be calculated. These measures include, for example, packet errorrate (PER), packet jitter and throughput. Similar to signal quality, inone embodiment the control subsystem 103 collects this information, andthen together with the radio transceiver 101 calculates measures such asPER, jitter and throughput.

In another embodiment, the radio transceiver 101 calculates thesemeasures on its own. In a further embodiment, the control subsystem 103together with the radio transceiver calculates a link quality score foreach base station based on a function which takes in one or more of linkquality measures such as PER, jitter and throughput as inputs, andproduces the score as the output. For example, in one embodiment thecontrol subsystem 103 calculates a weighted average based on PER andjitter. In another embodiment, a weighted average is first calculated,then compared against a threshold, and used to calculate a performancescore.

In another embodiment, in optional step 601, the control subsystem 103uses geo-location information, for example, the location of themobile/nomadic device relative to the base-stations, to select thesubset of the available channels and beams. In yet another embodiment,positional/motion information obtained, for example, from sensors in themobile/nomadic device are used by the control subsystem 103 in optionalstep 601 to select the subset of the available channels and beams.Examples of positional/motion information include velocity of thedevice, acceleration of the device, direction of travel of the device,orientation of the device, angular velocity of the device, angularacceleration of the device and altitude of device. In yet anotherembodiment, the subset of the available channels and beams is selectedby control subsystem 103 based on user input and instructions.

In yet another embodiment, the subset of the available channels andbeams is selected in optional step 601 based on at least one ofhistorical signal quality, geo-location information, userinput/instructions and positional/motion information.

In yet another embodiment, in optional step 601 the control subsystem103 uses the fact that the beams are overlapping to select a subset ofbeams to perform scanning.

Steps 602-604 detail the scanning process. In step 602, the controlsubsystem 103 determines the best-performing combination of basestation, channel and beam. It does so by attempting to establishwireless test links to base stations, using a set of candidate channelsand beams comprising at least some of the one or more availablechannels, and some of the one or more available beams. In oneembodiment, the candidate set is all available channels and beams. Inanother embodiment, the candidate set is the subset of channels andbeams selected using one of the methods outlined above.

For each wireless test link that the control subsystem 103 successfullyestablishes with a base station, the control subsystem 103 collectsinformation relating to signal quality of the test link. As previouslyexplained, signal quality can be measured by SNR, SINR or BER. Inanother embodiment, the control subsystem 103 uses the test link tocollect information including, but not limited to, link quality, basestation operating capacity; and base station load/utilization.

The control subsystem 103 then measures the performance for thecombination of base station, channel and beam. In one embodiment,performance is measured by signal quality. As previously explained,signal quality can be measured by SNR, SINR or BER.

In one embodiment the control subsystem 103 together with the radiotransceiver 101 calculates SNR, SINR and BER. In another embodiment, theradio transceiver 101 calculates these measures on its own. In analternative embodiment, the control subsystem 103 together with theradio transceiver 101 further calculates a signal quality score based ona function which takes in one or more of signal quality measures such asSNR and SINR as inputs, and produces the score as the output. Oneexample of such a function is a weighted average. Another example ofsuch a function is where a weighted average is first calculated, thencompared against a threshold, and used to calculate a performance score.

In another embodiment, performance can be measured by calculating ascore for each combination based on a function which takes in one ormore of signal quality measures such as SNR and SINR; link qualitymeasures such as PER, jitter and throughput, base station operatingcapacity; and base station load/utilization as inputs, and produces thescore as an output. For example, in one embodiment, the controlsubsystem 103 calculates a weighted average based on SINR, base stationoperating capacity; and base station load/utilization; and selects thebase station with the best weighted average. In another embodiment, thecontrol subsystem 103 first calculates the weighted average, thencompares against a threshold, and uses the comparison to calculate afinal performance score.

FIG. 6A shows one embodiment to perform step 602 for a candidate set ofchannels and beams. In FIG. 6A, control subsystem 103 scans all channelsin the candidate set, and for each channel, all available beams in thecandidate set. In step 620, control subsystem 103 selects a firstchannel and a first beam from the candidate set. In step 621, controlsubsystem 103 attempts to establish a test link to a base station usingthe first channel and the first beam in the candidate set. If this issuccessful, (step 622) then in step 623 the control subsystem 103records performance for every base station, channel and beam for which atest link is successfully established.

In step 624, the control subsystem 103 checks to see if all beams havebeen used. If not, then, in step 625, the control subsystem 103 selectsthe next beam in the candidate set and returns to step 621. If all beamshave been used, then in step 626 the control subsystem 103 checks to seeif all channels have been used. If not, then in step 627, the controlsubsystem selects the next channel in the candidate set and returns tostep 621. If all channels have been used, the control subsystem 103 thenmoves to step 603.

In another embodiment in step 602, the control subsystem 103 scans beamsin the candidate set, and for each beam, it scans all channels in thecandidate set.

Once this is complete, then in step 603 the control subsystem 103 buildsa list showing performance for all combinations of base station, channeland beam.

In step 604 the control subsystem 103 selects the best performingcombination of base-station, channel and beam based on the informationit collected in steps 602 and 603.

At the end of the scanning process, in step 605, the control subsystem103 then establishes an operating link to the selected base-stationusing the selected operating channel and beam. Communication over theoperating link is carried out in step 606. In a further embodiment, ifthe operating link is not successfully established in step 605, then thecontrol subsystem 103 establishes an operating link to the next bestcombination of base station, operating channel and beam, andcommunication over the operating link is carried out in step 606.

In one embodiment, as shown in FIG. 6B, in step 610, when the smartantenna system 100 becomes active, the control subsystem 103 configuresthe radio transceiver 101 first, and then the antenna subsystem 102 toconnect with the base station and establish an operating link on thechannel and with the beam on which an operating link was lastestablished. If operating link establishment fails (step 610A), thencontrol subsystem 103 performs steps 612-616, which are similar to steps602-606 described above. In one embodiment, similar to as describedpreviously for step 601, control subsystem 103 may optionally performstep 611, which is selecting a subset of the available channels andbeams for the candidate set in step 612.

In one embodiment, after the operating link is established the basestation, channel and beam selection remain fixed until the operatinglink is lost. Once the operating link is lost, the control subsystem 103performs steps 602-606 of FIG. 6. In one embodiment, similar to asdescribed previously, control subsystem 103 additionally performs step601.

In another embodiment, after the operating link is established, thecontrol subsystem 103 performs tracking, that is, the control subsystem103 continues to search for a better combination of base station,channel and beam than the currently selected combination of basestation, operating channel and beam. In one embodiment, the controlsubsystem 103 performs tracking in the background; while communicationover the currently established operating link is ongoing.

FIG. 6C shows a sequence of steps involved in tracking

An example situation where tracking is useful is shown in FIGS. 6D-6F.As a mobile device changes its position relative to the base-station towhich is connected, it is possible that the currently selected beammight no longer be the optimum one. FIGS. 6D and 6E show an example ofsuch a situation. In FIG. 6D, the mobile device 904 uses beam 906 toconnect to base-station 901 because doing so would avoid interferencefrom base-stations 902 and 903 and therefore offers the best SINR.

However, as the mobile device moves in direction 907 the beam 906 will,at a certain point, offer worse SINR than beam 905 because ofinterference from base-station 903. FIG. 6E shows the same mobile device904 after it moved in direction 907 enough that the optimal beam is nowbeam 905 instead of beam 906. FIG. 6F shows the same mobile device 904after further moving in direction 907 enough that the optimumbase-station is no longer base-station 901 on beam 905 but base-station903 on beam 906. In such a situation, tracking would be useful to selecta beam with better performance.

In a further embodiment, the control subsystem 103 optionally performsstep 631 of FIG. 6C, that is, it selects a new subset of channels andbeams to be used in the tracking process using at least one of signalquality, geo-location and positional/motion information as outlinedabove.

In another embodiment, in step 631, positional/motion information,examples of which have been previously detailed, can be used togetherwith geo-location information of the device to predict the path of thedevice, and orientation of the device along this predicted path. Basedon this predicted path/orientation and other information such asgeo-location information of the base stations; subsets of the basestations, beams and channels which are likely to provide better links inthe future can be pre-loaded for tracking. For example, with referenceto FIGS. 6D-6F, if the positions of base stations 901, 902 and 903 areknown, then based on the orientation of device 904, the direction ofmotion 907 of device 904, and the beam patterns, it is possible todetermine the regions of coverage, and the interference which is likelyto be experienced if the device continues on the same path. A predictionis then made that either one of beam 905 and beam 906 will be used. Thecandidate subset of beams and channels can be narrowed to either beamdepending on which one is being used. For example, if beam 905 is beingused, then the candidate subset of beams and channels is narrowed tobeam 906. If the velocity and acceleration of device 904 is also known,then the instant at which the beam switch should occur can also bepredicted. In another embodiment, predicted path and orientation arecalculated by a subsystem external to the smart antenna, and thisinformation is communicated to the smart antenna to be pre-loaded forthe tracking process.

In step 632, the control subsystem 103 determines performance for allcombinations of base station, channel and beam other than the currentlyselected combination. In one embodiment, similar to step 602, it does soby using a candidate set of channels and beams to establish test linksto base stations. In one embodiment, the candidate set is the subset ofbeams and channels previously selected in step 601 of FIG. 6. In anotherembodiment, the candidate set is the subset of beams and channelsselected in optional step 631. In yet another embodiment, the candidateset is the set of all available channels and beams.

In one embodiment, in step 632 the control subsystem 103 performs steps620-627 of FIG. 6A for all combinations of base station, channel andbeam other than the currently selected combination.

In another embodiment, in step 632, control subsystem 103 searches for abetter beam by testing the performance of other beams while theoperating link is running on the currently selected beam. In oneembodiment, the control subsystem 103 only tests the performance ofdifference beams, and keeps the base station and operating channel thesame. In one embodiment, control subsystem 103 performs searching byperiodically instructing the antenna subsystem 102 to switch between thecurrently selected beam and its neighbors to detect if any of theneighboring beams offer a better signal quality. In one embodiment, thecontrol subsystem 103 alternates between adjacent beams. For example, inFIG. 6G, beam 915A shown by the solid line is the currently used beam.Beams 915B and 915C are adjacent to 915A. Beam 915D is adjacent to beam915B, and 915E are adjacent to beam 915C. Then, testing will alternatebetween beam 915B and beam 915C. This switching can be carried out, forexample, during a period between data transmissions such as for example,a gap between packets or bursts of packets. In another embodiment, thesegaps or periods are inserted between data transmissions to specificallyallow such switching to occur.

FIG. 6H shows a sequence where these gaps or periods, or morespecifically, tracking downtimes are inserted between data transmissionsto specifically allow such switching to occur. In one embodiment, thetracking downtime is fixed. In another embodiment, in step 641, controlsubsystem 103 calculates the duration of the impending trackingdowntime. In one embodiment, the duration of the period of trackingdowntime is set such that it is short enough not to affect the latencyof the user traffic. In one embodiment, the utilization of the down-linkand the up-link is first determined. Once this utilization iscalculated, then using known formulas, the average latencies fordifferent tracking downtime periods can be estimated. In one embodiment,in order to obtain the estimates, the average latency can beapproximated by the sum of

the average time from which a given packet arrives in the buffer untilthe end of the downtime; and

the average time taken to clear all the packets which are ahead of thegiven packet.

Both these average times can be calculated using formulas known to oneof skill in the art. Then, the estimated average latency for eachtracking downtime duration can be compared to a threshold latency. Thetracking downtime duration can be chosen such that the estimated averagelatency is less than the threshold.

In step 642, control subsystem 103 notifies, for example, the controlsubsystem of the current base-station of the impending trackingdowntime.

In step 643, upon receiving the notification the control subsystem ofthe base-station ensures that it will not schedule any down-link(base-station to device) or up-link (device to base-station)transmission to or from the notifying mobile device during the trackingdowntime. During the same period of time, the base-station buffers alldata packets that need to be delivered to the mobile device and anyother previously scheduled downlink or uplink scheduled allocations thathave been agreed with the mobile device. Also, the mobile device buffersall data packets that need to be delivered to the base-station and anyother previously scheduled downlink or uplink scheduled allocations thathave been agreed with the base-station.

In one embodiment, if the duration of the tracking downtime period isless than the minimum duration required to obtain a good measurement ofsignal quality for a single combination of base station, beam andchannel; then data is acquired over several periods until a sufficientamount of data has been acquired to obtain a good measurement of signalquality for a single combination.

In another embodiment, if the duration of the tracking downtime periodis greater than the minimum duration required to test a singlecombination of base station, beam and channel; then the controlsubsystem 103 will test two or more combinations of base station, beamand channel. The number of combinations tested is given by:

$N_{C} = \lceil \frac{{Tracking}\mspace{14mu}{downtime}}{{Minimum}\mspace{14mu}{duration}\mspace{14mu}{required}\mspace{14mu}{per}\mspace{14mu}{combination}} \rceil$where N_(C) is the number of combinations tested in a given trackingdowntime. For example, if it is determined that the minimum durationneeded to obtain good measurement of signal quality for a singlecombination is 1 ms and the tracking downtime duration is 1.2 ms, then 2channels are tested. If it is determined that the tracking downtimeperiod is less than the minimum duration needed to obtain goodmeasurements of signal quality for all the combinations within thecandidate set of beams and channels, then data is acquired over severalperiods until a sufficient amount of data has been acquired to obtaingood measurements of signal quality for all the combinations. Using theexample above, if it is determined that the minimum duration needed toobtain good measurement of signal quality for a single combination is 1ms and there are 2 combinations within the candidate set of beams andchannels, then the minimum duration needed to obtain good measurementfor both combinations is 2 ms. However, if the tracking downtimeduration is 1.2 ms, then data must be acquired over 2 durations toensure that a good measurement of signal quality can be obtained.

In another embodiment, if the duration of the tracking downtime periodis greater than the minimum duration required to test a singlecombination of base station, beam and channel; then the number ofcombinations tested is given by:

$N_{C} = \lceil \frac{{Tracking}\mspace{14mu}{downtime}}{{Minimum}\mspace{14mu}{duration}\mspace{14mu}{required}\mspace{14mu}{per}\mspace{14mu}{combination}} \rceil$

where N_(C) is the number of combinations tested in a given trackingdowntime. For example, if it is determined that the minimum durationneeded to obtain good measurement of signal quality for a singlecombination is 1 ms and the tracking downtime duration is 1.2 ms, thenonly one channel can be tested to ensure that a good measurement ofsignal quality can be obtained. Similar to as previously explained, ifit is determined that the tracking downtime period is less than theminimum duration needed to obtain good measurements of signal qualityfor all the combinations within the candidate set of beams and channels,then data is acquired until a sufficient amount of data is recorded, toobtain good measurements of signal quality for all the combinations.

In one embodiment, the control subsystem 103 tests the signal quality onthe neighboring beam using normal data packets on the neighboring beam.In another embodiment, the control subsystem 103 instructs the antennasubsystem 102 to switch from the currently selected beam to aneighboring beam during a period between data transmissions, and thentests the signal quality on the neighboring beam, using special channelsounding packets on the neighboring beam. Control subsystem 103 theninstructs the antenna subsystem 102 to switch back to the currentlyselected beam and resumes transmission of normal data packets. This isdone to ensure that the delivery of data packets is not affected in casethe signal quality on the neighboring beam is very poor.

In certain cases, the interference experienced may be periodic.Furthermore, some base stations operate periodically, alternatingbetween short “busy” periods and long “quiet” periods. If tracking isperformed periodically, there is a chance that tracking will only occurduring the “quiet” periods, and the base station will be “missed”.

To overcome these problems, in another embodiment, the mobile deviceperforms tracking at aperiodic intervals to remove the impact of thisperiodic interference on the SINR measurements. In one embodiment, theaperiodic intervals are pseudo-random.

In one embodiment, in optional step 633, the control subsystem 103builds a list showing performance for all combinations of base stations,channels and beams in step 633. As previously explained, performance maybe measured by signal quality or other measures, or a combination ofsignal quality and other measures. As has also been previouslyexplained, signal quality can be measured by, for example, SNR, SINR,BER, or a score calculated from a function which takes in measures suchas SNR and SINR as inputs, and produces the score as an output.

If, for example, using the list built in step 633, or otherwise, thecontrol subsystem 103 finds a better combination of base station,channel and beam than the currently selected combination of basestation, channel and beam (step 633A), then it moves to select thebetter combination in step 634. For example, in the embodiment describedabove with reference to FIG. 6G, if beam 915B offers better performancethan 915A, then control subsystem 103 selects beam 915B. If not, thenbeam 915C is tested. If 915C is found to be better, then controlsubsystem 103 selects beam 915C. In another embodiment, the controlsubsystem 103 selects the better combination in step 634, only if thecontrol subsystem 103 determines that the improvement in signal qualitypersists for a predefined period.

If not, then control subsystem 103 continues searching for a bettercombination of base station, operating channel and beam. In oneembodiment, this involves selecting a new subset of available channelsand beams (step 631).

After the control subsystem 103 has selected the better combination instep 634, in step 635 the control subsystem 103 establishes a newoperating link to the selected base station using the new channel andbeam.

In step 636, communication over the newly established operating linkbegins. Optionally, the candidate set of beams and channels will also beupdated. For example, with reference to FIG. 6G, if control subsystem103 communicates using beam 915B, then in the next tracking downtime,beams 915D and 915A will be tested. If control subsystem 103communicates using beam 915C, in the next tracking downtime, beams 915Eand 915A will be tested.

In another embodiment, the control subsystem 103 searches for a standbycombination of base station, channel and beam, in case the currentoperating link fails. In one embodiment, the control subsystem 103periodically performs steps 631-633 of FIG. 6C in the background. If thecurrent operating link fails, then the control subsystem 103 selects thebest combination of base station, channel and beam identified;establishes a new operating link over this combination; and communicatesover this newly established operating link.

The process outlined above to select base station, operating channel andbeam based on signal quality offers advantages over making decisionsbased on signal strength. An illustrative example of these advantages isshown in FIG. 7. FIG. 7 which shows a mobile device 701 containing asmart antenna system, with wireless test links to base stations 702 and703. Device 701 determines that base station 702 provides better signalquality than base station 703. Device 701 then has to select a beam. Itdecides to select beam 712 over beam 711, for the following reason:Device 701 can establish a test link to base station 702 with eitherbeam 711 or 712 because it is in the area 713 in which the two beamsoverlap. The signal strength for base station 702 using beam 711 isstronger than beam 712 because base station 702 is closer to the centerof beam 711. However, if the control subsystem 103 selected beam 711,then it would have to contend with interference from base station 703,and therefore the SINR would be lower. Control subsystem 103 choosesbeam 712 because it offers lower interference, and consequently a bettersignal quality, than with beam 711.

FIG. 8 shows the coverage for the base stations 401 and 402 of FIG. 2but with the mobile/nomadic devices 511 and 513 using smart antennas.Compared to FIG. 2 the coverage 503 for the base-station 401 and thecoverage 504 for the base-station 402 are much larger, almost coveringthe entire area of interest 405. Mobile device 511 selects beam 512 thatprovides good signal strength from base station 401 and provides goodisolation from (rejection of) base station 402, which means good SINRand therefore signal quality. Similarly mobile device 513 selects beam514 that includes base station 402 but excludes base station 401.

While particular embodiments and applications of the present inventionhave been illustrated and described, it is to be understood that theinvention is not limited to the precise construction and compositionsdisclosed herein and that various modifications, changes, and variationsmay be apparent from the foregoing descriptions without departing fromthe spirit and scope of the invention as defined in the appended claims.

The invention claimed is:
 1. A smart antenna system for communicatingwireless signals between a mobile device and a plurality of fixed basestations using one or more channels and one or more beams, said smartantenna system comprising a control subsystem, a radio transceiver andan antenna subsystem coupled to each other to perform scanning of one ormore combinations of base stations, channels and beams using one or moretest links established with one or more of said fixed base stations,said one or more test links using at least some of the channels and thebeams; select a first combination of base station, channel and beambased on data obtained during scanning; establish a first operating linkfor transmitting a wireless signal to the currently selected basestation using the currently selected channel and beam; and afterestablishing said first operating link, perform continued scanning usingone or more test links established with the currently selected basestation and channel, and one or more beams different from the currentlyselected beam, said one or more beams adjacent to the currently selectedbeam; and said continued scanning being performed either periodically oraperiodically.
 2. The system of claim 1, wherein if after performingsaid continued scanning using an adjacent beam, based on data obtainedduring said continued scanning using the adjacent beam, said adjacentbeam is found to have better performance than the currently selectedbeam, then said control subsystem establishes a second operating linkfor transmitting a wireless signal to the currently selected basestation, using the currently selected channel and said adjacent beam. 3.The system of claim 1, wherein before performing said continuedscanning, said control subsystem inserts a downtime, and said continuedscanning is performed during said downtime.
 4. The system of claim 3,wherein said control subsystem calculates the duration of the downtimebefore inserting said downtime.
 5. The system of claim 4, wherein saidcalculated duration of downtime is less than a threshold duration toobtain sufficient data to determine performance of one beam; and saidcontinued scanning is performed over more than one downtime untilsufficient data is obtained.
 6. The system of claim 5, wherein aplurality of beams are used in said continued scanning, said calculatedduration of downtime is less than a threshold duration to obtainsufficient data to determine performance of all beams within saidplurality of beams; and said continued scanning is performed over morethan one downtime until sufficient data is obtained.
 7. A method ofcommunicating wireless signals between a mobile device and a pluralityof fixed base stations using one or more channels and having one or morebeams, said method comprising scanning one or more combinations of basestations, channels and beams using one or more test links establishedwith one or more of said fixed base stations, said one or more testlinks using at least some of the one or more channels and the one ormore beams; selecting a first combination of base station, channel andbeam based on data obtained during the scanning; establishing a firstoperating link for transmitting a wireless signal to the selected basestation using the selected channel and beam; and after establishing saidfirst operating link, performing continued scanning using one or moretest links established with the currently selected base station andchannel, using one or more beams different from the currently selectedbeam, said one or more beams adjacent to the currently selected beam;and wherein said continued scanning is performed either periodically oraperiodically.
 8. The method of claim 7, wherein if after performingsaid continued scanning using an adjacent beam, based on data obtainedduring said continued scanning using the adjacent beam, said adjacentbeam is found to have better performance than the currently selectedbeam, then establishing a second operating link for transmitting awireless signal to the currently selected base station, using thecurrently selected channel and said scanned adjacent beam.
 9. The methodof claim 7, wherein prior to performing continued scanning, inserting adowntime, and said continued scanning is performed during said downtime.10. The method of claim 9, further comprising calculating the durationof the tracking downtime before inserting said downtime.
 11. The methodof claim 10, wherein said calculated duration of downtime is less than athreshold duration to obtain sufficient data to determine performance ofone beam, and said continued scanning is performed over more than onedowntime until sufficient data is obtained.
 12. The system of claim 10,wherein a plurality of beams are used in said continued scanning, saidcalculated duration of downtime is less than a threshold duration toobtain sufficient data to determine performance of all beams within saidplurality of beams, and said continued scanning is performed over morethan one downtime until sufficient data is obtained.